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[850tgul]

Hi all,
I just installed a new set of Arc-8 18x8.5et45, square setup, w/ 235/40 Hankook V12s today. '09 128i on stock sport suspension. Removed the oem 262 17" which had Pirelli Cinturato P7 all season run flats.

I had read that switching to non-run flats would make the ride more comfortable, and it did, but missed the part where it turned my 128i into a lincoln town car.

Fist thought was that I hadn't yet burned off the "factory finish" of the tires but I was downright scared at how floaty and loose the car was on the highway. I have swapped many a tire and never felt such a drastic difference.

Car also felt noticeably more sluggish, especially in 2nd gear. So I thought un-sprung weight increase. But according to Apex and Tire rack the new wheels/tire combo weighs 42.2 lbs per corner (24 lbs for the tire and 18.2 for the wheel) while my oem 262 staggered setup weighed in at 47 lbs front and 49.6 lbs rear ( weighed them myself). So I'm lost here.

Few other things to note. Shop didn't have time to do an alignment today, that is tomorrow and the current tire pressures are roughly 45 psi all around. Is that too high?

Really hope the alignment and wearing the tires in some will help with the handling but still somewhat concerned with the sluggishness. Sucks too because I absolutely love the way these wheels look on the car.

Any input would be helpful. Thx

[gregthegr8]

Originally Posted by 850tgul

Few other things to note. Shop didn't have time to do an alignment today, that is tomorrow and the current tire pressures are roughly 45 psi all around. Is that too high?

Start with the tire pressures since you can easily adjust that yourself. 45 is way too high. recommended pressures on a 128 with an 18" 215/245 set up should be 32 front, 39 rear. Not quite sure what you should adjust it to since you're running 235 square, but clearly less than 39 all around. Others probably have more information, but I'd start by dropping those air pressures considerably and seeing how that feels as a starting point.

[850tgul]

I'll start there, thanks. Thought 45 was a bit much.

[andrey_gta]

Alignment will help slightly. But it may be your shocks and in general noticing issues with suspension because of non runflats.

I suggest at the very least a front sway bar- it helped me have more accurate turn in.

Someone recently said on e90post that Rear shock mount kit from dinan helped them with softness/loose rear. There was a thread here in suspension forum too not too long ago.

Then there are inserts or subframe bushes

Rear top side m3 arms help a bit

And Koni sale until Aug 31 - you can get Koni Str.t kit for the shocks

In general pick a budget and see what mods work for you.

[Phlonx]

I thought the car felt pretty crappy with the run-flats, I can feel the hub just took too long to come down when suspension was compressed. Also, you can feel every little thing on the road, and that's not a good thing. It almost acted like car would hop, especially if I was turning and making the suspension dampen the bums on the road. When I got my Apex EC-7's and Conti DW's I saved quite a bit of weight all around. That being said, I immediately replaced the suspension because let's face it, it's not exactly sporty and yes it was tuned to work with run flats. Next mod is definitely the rear sub-frame bushings. At the moment if I'm turning at high speeds the rear end feels unsure of itself; and that's scary with about 400HP. I hear the bushings will make a world of difference.

[850tgul]

I read about the increased comfort and ride quality from switching to non-run flats, I suppose I just didn’t do enough research or I overlooked the drawbacks. Since about 99% of forum users completely rail against the run flats every chance they get, I figured the switch was a no brainer. Truth is, I’ve had some serious sports cars in the past that rode much stiffer than my 128 with run flats, so I never considered the ride unduly harsh. Even with my all season Pirellis run flats I was pleasantly surprised by the sharpness of the chassis, on the street anyway.

Now with the non-run flat Hankooks the body roll and general softness of the chassis is no longer masked by the run flat’s stiff sidewalls. The steering input is very slow and the high speed direction change is downright unnerving.

As I see it my options are now to upgrade my suspension to make the car handle like it did in the past or go back to run flats. Seeing as I won’t ever track my car, I’m seriously leaning towards the latter. Certainly be cheaper than getting M3 fsb, bushings,, rear subframe bushings etc.

[andrey_gta]

Originally Posted by 850tgul

Seeing as I won’t ever track my car, I’m seriously leaning towards the latter. Certainly be cheaper than getting M3 fsb, bushings,, rear subframe bushings etc.

None of those M3 bits are necessary. Shocks & maybe springs should fix this inaccuracy you describe hence why i said Koni Str.t a hard to beat package for 128i, it also has less rake in the front than 135i on same springs.

[3002 tii]

No reason to get an alignment. If your car wasn't pulling before and you didn't experience uneven tread, no reason to get the alignment now. The main issue of going to non-RFT is that it exposes how soft the oe suspension is. And if you don't have M-sport, it's probably even worse. Not sure how many miles you have on your oe shocks, maybe you're due for replacements but you'll still end up with a rather soft ride.

If you don't have M-sport, I'd see if you can snag someone's M-sport suspension. I see low mileage setups on classifieds all the time and they're pretty cheap. While you're at it, you could upgrade subframe bushings. I didn't go with M3 bushings but went with aftermarket inserts and I'm quite happy with them.

[850tgul]

Would very much like to stay at stock ride height, and with the 18x8.5et45 wheel up front, I think I'd have to to avoid rubbing and or fender/camber work. Any thoughts on an upgraded shock to work with the oem spring?? Was planning to do an upgraded fsb anyway, so perhaps the combo of some stiffer shocks and fsb would clean up a lot of the slop.

[gregthegr8]

Originally Posted by 850tgul

Would very much like to stay at stock ride height, and with the 18x8.5et45 wheel up front, I think I'd have to to avoid rubbing and or fender/camber work. Any thoughts on an upgraded shock to work with the oem spring?? Was planning to do an upgraded fsb anyway, so perhaps the combo of some stiffer shocks and fsb would clean up a lot of the slop.

You could go with something like a stock 135 suspension setup, or if want something a lil nicer/better could go with koni yellow shocks or the BMW performance suspension. The performance suspension comes with an upgraded front sway bar as well, though it does lower the car a very subtle 10mm compared to the stock 135 suspension at least.

There are a lot of people though that have full 135 suspensions out there available, as mine is sitting in a giant box in my bedroom after being on the car for only 6k miles. Many options. You could of course just opt back into some runflats for your new wheels and sell the hankooks on the forum perhaps.

[andrey_gta]

Originally Posted by 850tgul

Would very much like to stay at stock ride height, and with the 18x8.5et45 wheel up front, I think I'd have to to avoid rubbing and or fender/camber work. Any thoughts on an upgraded shock to work with the oem spring?? Was planning to do an upgraded fsb anyway, so perhaps the combo of some stiffer shocks and fsb would clean up a lot of the slop.

If your 128i does not have a sport package I can see how the soft/vagueness has come about. But regarldess if you do have the sport package an update can be had for a reasonable sum

OEM spring and a shock upgrade:
FSD koni
Koni yellow/Str.t
Bilstein HD
BMW perf

and what i did:
very lightly used 2011-2013 3 series e9x Msport/Sport shocks ( because BMW actually tried the most to fix them - 3rd revision for e9x) on 1 series springs like the H&R, Eibach, or even Vogland which are often very cheap (for 128i do not use 135i OEM front springs - they need the SP lowering perches to look okay and avoid any added height when compared to Sport 128i. Aftermarket 1 series springs like H&R/Swift actually look good on 128i). The shocks were surprisingly good upgrade from my aged 1 series Msport ( 115k km , 2008 production). If upgrading shocks, i recommend changing springs too cuz its the same process - 128 sport springs are even softer than 3 series 328i sport springs up front ( we have D3 they have D4 the stiffer version.)

[850tgul]

Updating for posterity's sake here. Swapped my oem runflats back on for the winter and the difference was much less drastic this time. I can only surmise that most of the looseness I felt when going from oem RFTs to new summer tires was due to the "factory finish" of the new summer tires.
Also, fwiw, my 18x8.5 et45, 235/40 never rubbed once on my stock sports suspension.

[Ginger_Extract]

the lighter/stiffer/wider wheels are giving you more direct feedback as to how poor the OE suspension is. You're experiencing what a lot of us found. Also, V12s have a pretty cushy sidewall, you're getting a bit of squirm there, as well.

[_Ryan_]

Originally Posted by 850tgul

I read about the increased comfort and ride quality from switching to non-run flats, I suppose I just didn’t do enough research or I overlooked the drawbacks. Since about 99% of forum users completely rail against the run flats every chance they get, I figured the switch was a no brainer. Truth is, I’ve had some serious sports cars in the past that rode much stiffer than my 128 with run flats, so I never considered the ride unduly harsh. Even with my all season Pirellis run flats I was pleasantly surprised by the sharpness of the chassis, on the street anyway.

Now with the non-run flat Hankooks the body roll and general softness of the chassis is no longer masked by the run flat’s stiff sidewalls. The steering input is very slow and the high speed direction change is downright unnerving.

As I see it my options are now to upgrade my suspension to make the car handle like it did in the past or go back to run flats. Seeing as I won’t ever track my car, I’m seriously leaning towards the latter. Certainly be cheaper than getting M3 fsb, bushings,, rear subframe bushings etc.

RFT tyres increase the effective spring rate.
Bushes can also increase the effective spring rate.
BMW softened bushes to allow them to run RFT and still feel like a luxury car. I didn't like my drive after switching tyres until I did the M3 arms and subframe inserts; whilst I did do my shocks/springs at the same time, the general feeling of 'tightness' was likely to be the bushes.

Take note of what the 'M' models ship with- solid rather than liquid filled bushes with 'normal' tyres.